In a small bowl mix the onion with a large pinch of salt and 1 tablespoon vinegar. Leave for 10 minutes.

Heat the remaining vinegar in a small frying pan with paprika, chilli flakes, tomato puree, spring onions and 4 tablespoons water. Bring to a simmer and cook for 2 minutes. Add the pork and cook over a very low heat for 5-6 minutes.

Mash the avocado roughly and mix with FAGE Total 2% yoghurt, orange juice and zest, season with pepper and spread onto the top half of both bread rolls. Add spinach and celery to the bottom halves.

Rinse the onions in cold water and pat dry on kitchen roll. Spoon hot pork onto the salad and top with onions.